1. Field of the Invention
The present invention relates to an optical pickup that is used to perform reading of information recorded on an optical disc and writing of information to an optical disc, and also relates to an optical disc apparatus that includes an optical pickup and performs reproducing of information recorded on an optical disc and recording of information to an optical disc.
2. Description of Related Art
Optical discs such as compact discs (hereinafter, called CDs), digital versatile discs (hereinafter, called DVDs), etc. have been widely used. Further, recently, optical discs such as Blu-ray discs (hereinafter, called BDs) and the like that can record large-size information have also been put to practical use. To carry out reproducing and recording of information from and to such an optical disc, an optical disc apparatus having an optical pickup is used.
FIG. 7 is a schematic plan view showing an optical pickup and related portions in a conventional optical disc apparatus. FIG. 8 is a view to explain relation between a teeth member and a lead screw used in a conventional optical pickup.
As shown in FIG. 7, a conventional optical pickup 101 has a first bearing portion 101a including two parts formed a predetermined distance away from each other at one end, and a second bearing portion 101b formed at the other end that is opposite to the one end. A first guide shaft 102a as a main shaft is inserted through the first bearing portion 101a, and a second guide shaft 102b as a sub-shaft is inserted though the second bearing portion 101b. Thus, the optical pickup 101 is slidable along the guide shafts 102a and 102b. 
The movement of the optical pickup 101 along the guide shafts 102a and 102b is carried out by an optical pickup drive mechanism 103. The optical pickup drive mechanism 103 has various structures, and for example, as disclosed in JP-A-2007-280463, the optical pickup drive mechanism includes a teeth member 1031, a lead screw 1032, and a screw motor 1033.
The teeth member 1031 is detachably mounted on the optical pickup 101 with a screw (not shown). As shown in FIG. 8, the teeth member 1031 is provided with a plurality of gear teeth 1031a. Besides, as shown in FIG. 8, the lead screw 1032 is provided with a spiral groove 1032a, which meshes with the gear teeth 1031a. Accordingly, if the screw 1032 is rotated by operation of the screw motor 1033, the optical pickup 101 moves along the guide shafts 102a and 102b. 
The guide shafts 102a and 102b are disposed extending in a longitudinal direction that is parallel to a radial direction of an optical disc (which is disposed at a position over the paper surface of FIG. 7, not shown, though). Thus, the optical pickup 101 is moved by the optical pickup drive mechanism 103 along the guide shafts 102a and 102b, so that the optical pickup 101 is able to access each address formed on an optical disc that rotates at high speed.
In the optical pickup composed as described above, recently, a base (hereinafter, called a slide base) that constitutes the optical pickup 101 is formed of a resin for cost reduction. If the slide base is formed of a resin, a part where a screw or the like is mounted is required to be thick from the viewpoint of strength compared with a slide base formed of a metal. Accordingly, the slide base becomes thick, and the entire optical pickup apparatus tends to become thick.
Specifically, it is becoming unavoidable to form the slide base thick on the part thereof where the above teeth member 1031 is fixed with a screw to the slide base of the optical pickup 101. This is explained with reference to FIG. 9. FIG. 9 is an enlarged perspective view showing the first bearing portion 101a and related portions of the conventional optical pickup 101.
As shown in FIG. 9, in the conventional optical pickup 101, for easy mounting of the teeth member 1031, a nut hold portion 1012 is formed on the side of a slide base 1011 to position and hold a nut 1013. The nut hold portion 1012 includes a placement surface 1012a on which the nut 1013 is placed, a positioning wall 1012b that has a shape fitting the shape of the nut 1013 and positions the nut 1013 placed on the placement surface 1012a, two coming-out prevention portions 1012c that protrude from a position of the positioning wall 1012b higher than the thickness of the nut 1013 and prevent the nut 1013 from coming out, and an insertion opening 1012d that allows the nut 1013 to be inserted in a direction substantially perpendicular to the longitudinal direction of the first guide shaft 102a. 
The nut hold portion 1012 is disposed under the guide shaft 102a, so that the nut hold portion 1012 does not obstruct the first guide shaft 102a when the first guide shaft 102a is inserted into the slide base 1011. If the coming-out prevention portion 1012c is formed thin, the coming-out prevention portion 1012c can be broken when the teeth member 1031 is fixed to the slide base 1011 with a screw. For this reason, the coming-out prevention portion 1012c needs to be formed thick to some extent. Accordingly, it is unavoidable to form the slide base 1011 thick to some extent because of the presence of the nut hold portion 1012.
However, a thin optical pickup apparatus is an important factor in raising the added value of the product, and the demand for a thin optical pickup apparatus is increasing in the market. Accordingly, in the conventional optical pickup, in forming the slide base 1011 of a resin, because the slide base 1011 cannot be formed so thick, the slide base 101 is sometimes broken when it is fixed with a screw. If the nut hold portion 1012 is structured complicatedly, it is possible to prevent the breakage at the time of fixing. However, such a complicated structure is a cause of cost increase such as increase in mold components at the time of fabrication and the like, which needs to be avoided.